The invention relates to a filter stack for use in a
for fluids which can be operated according to the cross-flow principle in accordance with the technology known from DE-OS 33 41 262. The stack-like separating element described therein and consisting of layered blanks between two end plates could be improved as regards its flow guidance if it is a question of achieving as low a pressure drop as possible between retentate entrance and retentate exit without this being at the expense of the filtration performance.
A certain pressure on the filtrate side is necessary in particular in the filtration of liquids with a high CO.sub.2 content like beer, fruit juices with a strong CO.sub.2 content and the like in order to avoid a degassing of CO.sub.2 from the liquid. This necessitates a rather high pressure level on the retentate side in order to make the filtration possible at all, that is, the entire filtration system must be pressure-stable toward the outside.
On account of the relatively small perforations in the stack-like separating element according to DE-OS 33 41 262, overflowing of the membrane is prevented by the strong pressure drop between retentate entrance and retentate exit. This can potentially bring about a rapid buildup of a cover layer with associated dropping filtration performance. In particular the approach flow openings tend to become blocked in the case of media with a high solid and particle component such as e.g. fruit juices and also in the case of a filtration of highly viscous liquids such as milk and whey.
It is also known from DE-GM 87 00 793 that bell-shaped filter elements consisting of ceramics can be stacked axially with spacing around a hollow core formed by them in a surrounding pressure housing and that the slots formed between the bell-shaped filter elements on the outer side and on the inner side can be flowed over in the direction of the jacket lines in accordance with the cross-flow principle. The removal of filtrate takes place from rim positioned hollow spaces in the ceramic bodies. As a result of the special shaping, the manufacture is limited to solid and form-stable materials and is very complicated.
The invention therefore has the task of creating with simple constructive means a filter device of the initially mentioned design, especially for the filtration of media with a high solid component or particle component, which can be operated at a rather high operating pressure, in which the pressure drop is relatively small within the flow paths and in which the use of various types of separating media in accordance with the same sealing principle of the individual elements is possible.